1. Field of the Invention
The present invention relates to the field of read circuits for magnetic media recordings. More particularly, the present invention relates to an interconnect circuit for a magnetic media disk drive.
2. Description of the Related Art
FIG. 1 shows a high RPM disk drive 10 having a magnetic read/write head (or a recording slider) that is positioned over a selected track on a magnetic disk 11 for recording data using a servo system. The stage servo system includes a voice-coil motor (VCM) 13 for coarse positioning a read/write head suspension 12 and may include a microactuator, or micropositioner, for fine positioning the read/write head over the selected track. FIG. 2 shows an enlarged exploded view of the read/write head end of suspension 12 in the case when a microactuator is also being used. An electrostatic rotary microactuator 14 is attached to a gimbal structure 15 on suspension 12, and a slider 16 is attached to the microactuator. A read/write head 17 is fabricated as part of slider 16.
A single-ended input (SE) preamplifier is preferred over a differential input (Diff.) preamplifier in a readout channel front-end for a disk drive because a single-ended preamplifier requires less chip area and costs less than a Diff. preamplifier for the same performance. For the same performance, the power dissipation of a single-ended preamplifier is lower than that of a Diff. preamplifier. Additionally, a single-ended preamplifier only requires a single power supply, whereas a Diff. preamplifier requires two supplies (a positive supply and a negative supply). For the same chip area, the signal-to-electronics-noise ratio of a single-ended preamplifier is higher. Nevertheless, a drawback associated with a single-ended preamplifier is that a single-ended preamplifier has an upper data rate that is limited by thexe2x80x9cxc2xc wavelength effectxe2x80x9d of thexe2x80x9creturnxe2x80x9d transmission line on the head suspension. This limitation is illustrated by FIGS. 3-5.
FIG. 3 shows a schematic block diagram of a conventional readout channel front-end for a disk drive. FIG. 4 shows a cross-sectional view of the conventional integrated trace suspension interconnect circuit shown in FIG. 3 between the (G)MR sensor and the SE preamplifier. In FIG. 3, a magnetoresistive (MR) head is connected to a single-ended preamplifier through a conventional integrated trace suspension interconnect circuit 30. The MR head is represented by a resistance Rmr and signal source Vmr connected in series. The MR head is connected to the SE preamplifier through traces, or lines, A and B. A stainless steel suspension SS is represented in FIG. 3 along each trace A and B. To achieve high bandwidth, it is necessary for the input impedance of the SE preamplifier to be close to the characteristic impedance of the interconnect circuit       Z    0    =                    L        C              .  
Even when the input impedance of the SE preamplifier is close to the characteristic impedance of the interconnect circuit, the bandwidth of the readout channel is always limited by the xc2xc wavelength notch of the shortedxe2x80x9creturnxe2x80x9d transmission line, as described below.
FIG. 4 shows a cross-sectional view of the conventional integrated trace suspension interconnect shown in FIG. 3. Traces A and B are each typically formed from copper, and disposed above stainless steel suspension SS adjacent to each other, that is, side-by-side. The widths of traces A and B are typically less than 50 xcexcm each and are separated from each other by about 50 xcexcm. Traces A and B are each separated from suspension SS by a dielectric material DM that is about 20 xcexcm thick. The dielectric constant ∈r of the dielectric material separating traces A and B from suspension SS is typically about 2.7.
The cross-sectional dimensions of traces A and B and the ∈r of the dielectric are always such that the energy travels predominantly between line A and suspension SS and between line B and suspension SS. The energy transfer by the transmission path formed by the A and B lines can be neglected. Consequently, FIG. 3 is an adequate representation of a conventional SE preamplifier readout channel. The xe2x80x9cforwardxe2x80x9d transmission line A/SS is terminated in the SE preamplifier by the characteristic impedance ZOA for obtaining maximum transfer bandwidth. The return transmission line B/SS is grounded at the (grounded) input of the SE preamplifier. For a length l and a propagation velocity vp at a frequency fn=vp/4l, the return line B presents an open input to the MR head (Rmr, Vmr), thereby creating a null in the frequency transfer characteristic from the head voltage Vmr to the SE preamplifier input voltage.
FIG. 5 is a graph showing the voltage transfer characteristic 51 as a function of frequency of the conventional interconnect circuit of FIGS. 3 and 4. A null 52 appears in the frequency transfer characteristic that is given by:
fn=Vp/4l=xc2xcxcfx84p=xc2xcl{square root over (LC)},
wherein xcfx84p is the propagation delay along return line B of length l, L is the distributed series inductance per meter of return line B, and C is the distributed parallel capacitance per meter of return line B. Additionally,       Z          0      ⁢      B        =            L      C      
and most often Z0B=Z0A, i.e., the line pairs are designed to be left/right symmetric, such as shown in FIG. 4.
For frequencies below fn, the xe2x88x923 dB point of the transfer characteristic shorted return line (trace B) constitutes a frequency-dependent inductor at the MR head input side. That is,       L    eq    =                    Z                  0          ⁢          B                            2        ⁢        π        ⁢                  xe2x80x83                ⁢        f              ⁢    tan    ⁢          xe2x80x83        ⁢                  (                              π            ⁢                          xe2x80x83                        ⁢            f                                2            ⁢                          f              n                                      )            .      
This inductance in series with the MR head causes a frequency roll-off of the transfer characteristic, as shown by curve 51 in FIG. 5. The presence of output-shored return line B, which is necessary for accommodating a single-ended amplifier, causes axe2x88x923 dB point in the extrinsic transfer (i.e., the signal transfer extrinsic to the electronics) given by:       f                  -        3            ⁢      d      ⁢              xe2x80x83            ⁢      B        =                              (                      xe2x80x83                    ⁢                                    R              mr                        +                          Z                              0                ⁢                A                                              )                /        2            ⁢      π      ⁢              xe2x80x83            ⁢              L        eq              =                            2          ⁢                      f            n                          π            ⁢      arctan      ⁢              xe2x80x83            ⁢                        (                                    2              ⁢                              R                mr                                                    Z                              0                ⁢                B                                              )                .            
Consider a numerical example in which l=5 cm and vp=0.6 vC. Thus, fn=900 MHz. For Rmr=Z0A=25 xcexa9, fxe2x88x923 dB=630 MHz. This is only the extrinsic bandwidth, that is, the signal transfer characteristic that is extrinsic to the electronics. The.overall bandwidth of the readout channel front-end (i.e., including the SE preamplifier) is narrower still.
The range for the characteristic impedance Z0 for the interconnect circuit is determined by the range over which the width of the traces can be varied and by the range over which the thickness and the xcex5r of the dielectric layer between the stainless steel suspension and the traces can be varied. First, the stainless steel suspension SS is not nearly as conductive as copper traces A and B, thereby causing skin-effect losses for the high-frequency signal content of the readout signal. Stainless steel suspension SS must be interrupted at certain places along traces A and B in order to accommodate hinges and gimbals that are part of a leaf-spring head suspension. The interruptions cause reflection points that further deteriorate the high frequency signal transfer characteristic of the interconnect circuit. The suspension/hinge/gimbal arrangement is not always sufficiently wide for accommodating two side-by-side read lines having a preferably low characteristic impedance Z0 (i.e., wide trace widths).
What is needed is a way to eliminate the xc2xc wavelength effect associated with a readout channel front-end for a disk drive employing an SE preamplifier, thereby increasing the data rate that can be transferred over an interconnect circuit between an MR head and a single-ended preamplifier.
The present invention eliminates the xc2xc wavelength effect associated with a readout channel front-end for a disk drive employing an SE preamplifier, thereby increasing the data rate that can be transferred over an interconnect circuit between an MR head and a single-ended preamplifier.
The advantages of the present invention are provided by an interconnect circuit for a readout channel front-end for a disk drive. According to the invention, the interconnect circuit includes a forward line and a return line. Both the forward line and the return line have a first end and a second end. The first end of both the forward line and the return line is connectable to a magnetoresistive head. The second end of both the forward line and the return line is connectable to a single-ended preamplifier. The return line is arranged to be disposed between the forward line and a suspension for a magnetoresistive head. A dielectric material, such as polyimide, is disposed between the forward line and the return line. The forward trace has a first predetermined width and the return trace has a second predetermined width that can be the same or different from the first predetermined width.
When the interconnect circuit is in a disk drive, the first end of the forward line is connected to a magnetoresistive head, and the second end of the forward line is connected to a single-ended preamplifier. Similarly, the first end of the return line is connected to the magnetoresistive head, and the second end of the return line is connected to the single-ended preamplifier. The return line is disposed between the forward line and a suspension for the magnetoresistive head. The characteristic impedance of the interconnect circuit is selected to be about equal to an input resistance of the single-ended preamplifier. Accordingly, the high-frequency roll-off of a transfer characteristic of the interconnect circuit is primarily determined by a high-frequency skin-effect loss in each of the forward and return lines and not by the much greater skin effect losses in the stainless steel suspension, and the transfer characteristic of the interconnect circuit does not exhibit a xc2xc wavelength effect notch.